Modern wireless mobile communication systems have two significant characteristics. The first one is broadband and high rate. For example, the fourth generation wireless mobile communication systems have up to 100 MHz of bandwidth and up to 1 Gbps of downlink rate. The second one is mobile interconnecting, which enables emerging services such as mobile internet, mobile video on demand, online navigation, and the like. These two characteristics have higher requirements on the wireless mobile communication technology, including ultrahigh rate wireless transmission, inter-area interference suppression, reliable signal transmission while moving, distributed/centered signal processing, etc. In the enhanced fourth generation (4G) and the fifth generation (5G) in the future, in order to meet the above development requirements, various key techniques have been proposed and discussed, and are worth extensive attention of researchers in the related field.
The enhanced fourth generation wireless mobile communication systems have generally the following development requirements:                Higher wireless broadband rate and optimization of local cell hot spots;        Further improved user experience, especially optimization of communication services for cell border areas;        Continuous researches on new techniques capable of improving spectral utilization, due to impossibility of 1,000 times of expansion of available spectrums;        Use of high frequency spectrums (5 GHz or even higher) to obtain large communication bandwidth;        Cooperation with existing networks (2G/3G/4G, WLAN, WiMax, etc.) to share data traffic;        Specific optimization for different traffics, applications and services;        Enhanced system capabilities for supporting large scale Machine Type Communications;        Flexible, intelligent and inexpensive network planning and deployment; and        Designs for saving power consumptions of networks and UE batteries.        
In order to achieve the above development requirements, the 3rd Generation Partner Project (3GPP) organization has discussed and accepted Device-to-Device (D2D) communication technique as a key technique in the enhanced fourth generation wireless mobile communication systems.
The D2D technique allows local communications or peer-to-peer communications, without access to core networks. With transmissions based on the D2D technique, loads on base stations can be effectively reduced and life time of mobile terminal batteries can be effectively prolonged. Generally, according to the whether there is coverage of a macro base station in the environment where UEs for D2D transmissions (referred to as D2D UEs hereinafter) are located, scenarios for the D2D UEs can be divided into network coverage, no network coverage and partial network coverage. In the partial network coverage scenario, there are D2D UEs with network coverage and D2D UEs without network coverage.
Currently, for D2D communications, especially those with coverage of base station, 3GPP has decided to use Physical Downlink Control Channel (PDCCH) and Enhanced PDCCH (EPDCCH) for transmitting D2D grant information for D2D Scheduling Assignment (SA) and D2D data. However, there is no specific solution regarding how to use the existing PDCCH and EPDCCH to schedule D2D SA and D2D data, particularly which time-frequency resource positions are to be used to transmit D2D SA and D2D data.
There is thus a need for new indications from the base station, or predefined schemes, to solve the problem regarding which time-frequency resource positions are to be used to transmit D2D SA and D2D data.